Comment # 17 on bug 894636 from Christian Wittmer

so after long time of 'brainstroming' ... I prefer the following solution:

squid.logrotate file:
### for systemd
/var/log/squid/access.log /var/log/squid/store.log /var/log/squid/cache.log {
    compress
    dateext
    maxage 365
    rotate 99
    size=+4096k
    notifempty
    missingok
    create 640 squid root
    sharedscripts
    postrotate
     /usr/bin/systemctl -q is-active squid.service && /usr/sbin/squid -k rotate
    endscript
}

### for SysVinit
/var/log/squid/access.log /var/log/squid/store.log /var/log/squid/cache.log {
    compress
    dateext
    maxage 365
    rotate 99
    size=+4096k
    notifempty
    missingok
    create 640 squid root
    sharedscripts
    postrotate
     /etc/init.d/squid reload
    endscript
}

if you agree I will prepare a maintenance Request then.